1. Field of the Invention
The present invention relates to a projection-type display apparatus.
2. Description of the Related Art
In one conventional projection-type display apparatus, a laser beam emitted from a laser beam source is modulated in intensity with a modulating signal by a light modulator, and a first-order diffracted beam from the light modulator is introduced as a projecting beam into a light beam scanning system which applies the projecting beam to scan a screen two-dimensionally for thereby projecting an image on the screen.
Since the first-order diffracted beam produced by the light modulator has a higher extinction ratio than a zero-order diffracted beam which is also emitted from the light modulator, the zero-order diffracted beam is cut off by a prism or a pinhole, and only the first-order diffracted beam is employed as a projecting beam. However, the brightness of the overall screen is limited because the maximum intensity of the first-order diffracted beam is determined by the modulation efficiency and the beam intensity can be modulated only within the modulation range of the first-order diffracted beam.
The extinction ratio referred to above is the ratio Imin/Imax (or its reciprocal) of a minimum value Imin to a maximum value Imax which can be assumed by the intensity of an output light beam which is modulated.